3.5x2 document size changes to 8.5x11 when reaching CWS 5.5.0.35

We have an old workhorse G4 Mac 9.2.2 that will send 3.5" x 2" documents (native .ai .psd .indd .pgm or .pdf etc.) to the CWS5 (PC Windows 7) which retains the 3.5" x 2" size and allows easy subsequent imposition to 24 up on 12" x 18" sheets for the Xerox 700 DCP. Can't repeat this process with newer intel iMac 10.6.8. Though the document size and page size in the native apps and/or pdf on the iMac are set to the 3.5" x 2" size, when the files reach CWS5 the properties show the page size as 8.5" x 11 not 3.5" x 2"--therefore CWS5 can't impose 24 up or any other up for that matter. Any input will be appreciated.